FM demodulation is routinely performed using analog signal processing techniques. Recently, techniques have developed which allow an analog communications signal to be processed using digital signal processing techinques. These techniques include methods which may involve phase sampling and discriminating an incoming signal to recover message information. Typically, quadrature mixing is employed to recover the message information. A major problem exists with these types of digital signal processing techniques. They provide a receiver structure which inherently exhibits a narrow dynamic range. Since the processed signal exhibits a narrow operational signal dynamic range, additional processing is required to handle signals having large dynamic range, usually resulting an AGC stages added to the digital receiver structure.
Throughout the literature pertaining to the implementation of digital FM demodulators, the most common techniques cited involve either monitoring signal zero crossing, or a more conventional type of signal discrimination such as quadrature detection. Both of these approaches involve calculation of signal power, which limits the usable signal dynamic range which is processed by the FM demodulators.
These approaches have several disadvantages, some of which are the complexity and signal processing overhead required to implement the necessary gain control of the incoming signal, and the resulting narrow dynamic range of the FM detector. The characteristics of prior digital FM demodulators also produce an output signal having non-linearities introduced by the limitations of the demodulation technique.